Computer printer technology has evolved to a point where very high-resolution images can be transferred to various types of media, including paper. One particular type of printing involves the placement of small drops of a fluid ink onto a media surface in response to a digital signal. Typically, the fluid ink is placed or jetted onto the surface without physical contact between the printing device and the surface. Within this general technique, the specific method that the ink-jet ink is deposited onto the printing surface varies from system to system, and can include continuous ink deposit and drop-on-demand.
With regard to continuous printing systems, inks used are typically based on solvents such as methyl ethyl ketone and ethanol. Essentially, continuous printing systems function as a stream of ink droplets that are ejected and directed by a printer nozzle. The ink droplets are directed additionally with the assistance of an electrostatic charging device in close proximity to the nozzle. If the ink is not used on the desired printing surface, the ink is recycled for later use. With regard to drop-on-demand printing systems, the ink-jet inks are typically based upon water and solvents such as glycols. Essentially, with these systems, ink droplets are propelled from a nozzle by heat or by a pressure wave such that all of the ink droplets ejected are used to form the printed image.
There are several reasons that ink-jet printing has become a popular way of recording images on various media surfaces, particularly paper. Some of these reasons include low printer noise, capability of high-speed recording, and capability of multi-color recording. Additionally, these advantages can be obtained at a relatively low price to consumers.
Though there has been great improvement in ink-jet printing technology, as described previously, there are still improvements that can be made in many areas. Poor color durability has partially been alleviated by the incorporation of stabilizer molecules, or photo-stabilizers, into ink-jet inks. However, ink-jet ink chemistry itself as well as ink-jet ink/print media interaction have both contributed to the separation of colorant, i.e., dyes and/or pigments, and photo-stabilizers upon printing. With respect to ink-jet ink chemistry, the majority of commercial ink-jet inks are water-based. Thus, their constituents are generally water-soluble, as in the case with many photo-stabilizers and dyes, or water dispersible, as in the case with pigments. Furthermore, ink-jet inks have low viscosity (typically 5 cps or less) to accommodate high frequency jetting and firing chamber refill processes common to ink-jet pens. The high jetting shear force imposed on the ink can cause an initial separation of a dye, another liquid vehicle component, and/or a photo-stabilizer components of the ink-jet ink. Further, with respect to the relationship between a photo-stabilizer-containing ink-jet ink and a print media sheet, e.g., porous coated media sheet, additional and more permanent separation of the ink-jet ink components can occur chromatographically as the ink-jet ink penetrates the media surface. Thus, there exists challenges related to utilizing photo-stabilizers as effectively as possible within ink-jet ink formulations.
In addition to color and general image fade, ink-jet prints have also been known for poor durability when exposed to water or high humidity. This results from the use of water-soluble and water dispersible colorants within the water-based ink. There has been great improvement in the area of water durability of ink-jet inks through incorporation of certain ink-jet compatible latex polymers. The latex can consist of small micron or submicron hydrophobic polymeric particles of high molecular weight that are dispersed in the aqueous ink-jet ink. When printed as part of an ink-jet ink, a latex component of the ink can form a film on a media surface, entrapping and protecting the colorant within the hydrophobic print film.